Tunable matching networks are expected to play an important role in the realization of adaptive and reconfigurable radio front-end architectures. One particular example is the compensation of handset antenna impedance mismatch loss caused by user proximity effects using tunable antenna impedance matching networks.
Different matching network topologies have been reported in the literature. Basic L-type networks are able to achieve conjugate matching over a limited Smith chart region. On the other hand, pi-networks provide an extra degree of freedom that enables conjugate matching over a substantially wider impedance range. In the ideal case where the component values range is unbounded [0,∞], pi-networks can provide complete Smith Chart coverage and the component values for perfect conjugation matching can be calculated by using approaches known in the art.
The finite nature of the component tunable range is due to practical implementation limitations such as parasitic influences and component properties. For a matching network with finite component tuning ranges the perfect conjugate match can be achieved only if the load impedance lays within the matching domain. In reality, the network component available range may be predetermined and the unknown load impedance may often be located outside of the matching domain. Therefore, in practical impedance tuners with finite component tuning range, where a perfect conjugation match may not exist, optimization techniques have been commonly used to minimize the reflected signal (e.g., minimize VSWR). Different optimization approaches, such as simplex and single step, genetic method, or simulated annealing have been used to minimize the network input reflection coefficient as much as possible or at least down to an acceptable level. These optimization methods search for the right component tuning setting through an iterative process, consuming a considerable amount of time to reach the tuning goal. In addition, depending on the optimizer choice and its initial settings, there is a risk of converging into local minima.
Thus it is desirable to develop a deterministic approach to directly compute the final component tuning setting for the impedance match in order to reduce the tuning time and avoid the intermediate tuning states. A key aspect for such a tuning approach is a method to determine the load impedance, which also determines the equivalent admittance and complex reflection coefficient. It is desirable that determining the load determination is accomplished with minimal added loss, size and complexity.